Reconditioning oil used in cold working metal

ABSTRACT

Used non-aqueous metalworking lubricant, such as, cold rolling oil, is reconditioned by contacting it with sufficient strong base in the form of particulate or dissolved alkanol-soluble alkali metal hydroxyde and monohydric alkanol to reduce the total acid number of the oil to less than about 0.12 mg. KOH per gram of oil and preferably less than about 0.08 mg. KOH per gram of oil. At about 0.025 mg. KOH per gram of oil to zero total acid number the oil becomes a light golden color. On filtering or centrifuging the oil to remove precipitate formed during the strong base treatment, the oil is clarified and the ash content is reduced. If the oil already contains alkanol, only the strong base need be added as by suspending pellets of strong base in the oil in a cloth bag or wire screen enclosure or by circulating the coil through a charge of the particulate strong base. The reduced total acid number is maintained by steadily or periodically contacting the oil with strong base in the presence of monohydric alkanol. An improved combination for handling the oil comprises a cold rolling mill with a circulating lubricant system including a sump, a circulating pump, a reservoir and nozzle arrays immediately adjacent the rolls of the mill, and oil conduits operatively connecting the parts of the system, and, a charge of cold rolling oil, and in combination therewith, either a foraminous enclosure containing solid particulate strong base positioned in said charge of rolling oil, or a vessel holding a charge of particulate strong base and connected in series in the circulating lubricant system. Preferably, the combination also includes a filter or a centrifuge for removing solids such as those generated by the action of the strong base.

United States Patent Loftus [451 Feb. 19, 1974 RECONDITIONING OIL USED IN COLD WORKING METAL [75] Inventor: Thomas J. Loftus, Caseyville, Ill.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: Sept. 9, 1971 [21] Appl. No.: 179,072

[52] US. Cl. 208/183, 208/179 [51] Int. Cl Cl0m 11/00 [58] Field of Search 208/205, 184, 183, 179

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 742,909 l/19S6 Great Britain 208/281 1,041,703 9/1964 Great Britain 208/281 Primary ExaminerPaul M. Coughlan, Jr. Assistant ExaminerJuanita M. Nelson Attorney, Agent, or Firm-Edward E. Schilling 5 7] ABSTRACT Used non-aqueous metalworking lubricant, such as, cold rolling oil, is reconditioned by contacting it with sufficient strong base in the form of particulate or dissolved alkanol-soluble alkali metal hydroxyde and monohydric alkanol to reduce the total acid number of the oil to less than about 0.12 mg. KOl-l per gram of oil and preferably less than about 0.08 mg. KOH per gram of oil. At about 0.025 mg. KOI-l per gram of oil to zero total acid number the oil becomes a light golden color. On filtering or centrifuging the oil to remove precipitate formed during the strong base treatment, the oil is clarified and the ash content is re duced. If the oil already contains alkanol, only the strong base need be added as by suspending pellets of strong base in the oil in a cloth bag or wire screen enclosure or by circulating the coil through a charge of the particulate strong base. The reduced total acid number is maintained by steadily or periodically contacting the oil with strong base in the presence of monohydric alkanol.

An improved combination for handling the oil comprises a cold rolling mill with a circulating lubricant system including a sump, a circulating pump, a reservoir and nozzle arrays immediately adjacent the rolls of the mill, and oil conduits operatively connecting the parts of the system, and, a charge of cold rolling oil, and in combination therewith, either a foraminous enclosure containing solid particulate strong base positioned in said charge of rolling oil, or a vessel holding a charge of particulate strong base and connected in series in the circulating lubricant system. Preferably, the combination also includes a filter or a centrifuge for removing solids such as those generated by the action of the strong base.

14 Claims, 4 Drawing Figures Z0 25 gb Ff/fe r 0r RECONDITIONING OIL USED IN COLD WORKING METAL BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method and apparatus for reconditioning and maintaining used non-aqueous metal-working lubricant, such as, cold rolling oil of the type used for cold rolling metal such as aluminum or steel, especially as to reduction of the acidity and/or the ash content of the oil.

2. Discussion of the Prior Art A clean cold rolling lubricant, typically a mineral oil, is very important in rolling a quality product, and becomes extremely important in rolling thinner gauges of metal such as aluminum foil stock. Any dirt in the system will cause severe defects in the rolled metal which become more apparent as lighter gauges are made as rolling progresses and result in pin holes in the final product or tearing in the foil gauge range. Dirt is defined as solid particulate matter. The chief source of dirt in the oil in most rolling mill operations is the metal and non-metal particles or fines that are generated at the roll bite during differential slippage between the rolls and the metal slab or sheet being rolled.

The larger fines are reduced by settling and/or relatively coarse filtering the used oil through a paper filter. The finer particles remain suspended and also pass through a coarse filter and form a very stable colloidal dispersion. These minute particules accumulate steadily on repeated use of the oil and darken the color thereof as well as increase the ash content, some of the fines being oxidized during subsequent exposure to heat and air at the bite of the rolls as the lubricant is sprayed thereon.

Another problem encountered in cold rolling lubricants is the increase of acidity as the coolant is used and repeatedly re-used. Increased acidity is caused mainly by deterioration of the rolling oil as by oxidation or by direct contamination by tramp oils leaking into the lubricant system. Increasing acidity increases the likelihood of staining the metal product, such as white staining of aluminum, the result of a chemical attack which is almost impossible to remove and is most pronounced on bright surfaces. Staining such as white staining reduces the value of the product and sometimes makes the product unsalable.

Similar problems obtain in other metalworking operations using a non-aqueous lubricant.

For the purposes of the following description and claims, the term non-aqueous metalworking lubricant is considered to encompass non-aqueous lubricam for grinding, cutting and machining operations, as well as cold rolling and forming operations.

The usual method of dealing with the above problems is to periodically throw away a portion of the used oil and replace it with fresh clean oil thus diluting the dirty oil. However, such method has become unacceptable if it involves merely dumping the oil, and expensive if the oil must be disposed of in an acceptable manner.

Some operators filter the used oil through a diatomaceous earth filter but this, without more, does not reduce the acidity of the oil and the ash content is not as greatly reduced as would be desired unless a very fine earth is used in which case there is a tendency to absorb out beneficial additives typically employed in such an oil.

OBJECTS OF THE INVENTION The principal objects of the invention are to provide a practical method and an apparatus for reducing the total acid number of used non-aqueous metalworking lubricant without creating new problems, preferably while also reducing the ash content of the lubricant.

SUMMARY OF THE INVENTION It has now been discovered that upon contacting used, non-aqueous metalworking lubricant, such as cold rolling oil, with an alkanol-soluble alkali metal hydroxide in the presence of monohydric alkanol in a sufficient amount and for a sufficient time until the total acid number is reduced to less than about 0.12 mg. KOH per gram of oil, and preferably less than 0.08 mg. KOH per gram of oil, the oil is reconditioned. Desirably the hydroxide treated oil is also subjected to a mechanical separation process to remove precipitate formed during treatment with the strong base. Further continuous or intermittent treatment with the strong base in the presence of the alkanol maintains the low total acid number. The strong base is preferably potassium hydroxide, sometimes referred to as caustic potash.

The novel method is sometimes carried out using an alcoholic solution of the alkali metal hydroxide, but where the oil normally contains a monohydric alkanol, the process is carried out with apparatus for bringing solid particulate alkali metal hydroxide into intimate contact with the oil. Thus, the apparatus may comprise a rolling mill and associated circulating system for collecting and recycling the oil to the rolls, a charge of oil, and, in combination therewith, a foraminous enclosure containing solid particulate strong base positioned in the charge of oil. Preferably, the combination also includes means for mechanically separating solids from the strong base treated oil.

The apparatus, wherein a circulating lubricant system is used, may include means for circulating all or a by-pass stream of the circulating used lubricant through a charge of particulate alkali metal hydroxide held within an enclosed zone.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the apparatus combination of the invention including the foraminous enclosure for particulate strong base.

FIG. 2 is an enlarged foreshortened view, partly broken away and in section, of the foraminous enclosure shown in FIG. 1.

FIG. 3 is a view similar to FIG. 2 showing a different type of foraminous enclosure, here, a cloth bag.

FIG. 4 is a fragmentary portion of a schematic view similar to FIG. 1, illustrating another embodiment of the invention in which circulated oil is flowed through a charge of hydroxide particles.

DESCRIPTION OF THE INVENTION The method of the invention is applicable to any nonaqueous cold rolling oil or metalworking oil that is recycled after use, for example, in rolling, cutting, honing, grinding, abrasive finishing, machining or drawing metal, or in any other use for an extended period in a service such as, use as a hydraulic fluid, wherein the oil or components thereof are subject to oxidation. The

method is particularly useful and beneficial wherein particles of metal and of metal oxide, heavy grease, soil particles and other dirt regularly enter the oil. Typically, the oil is a mineral oil such as Generex 57 oil sold by Mobil Oil Company or Texaco 1527 oil sold by Texas Oil Company, but non-aqueous vegetable oils and blends thereof including mainly palm oil are also used as rolling or metalworking oil that is benefited by treatment according to the invention.

The method of the invention is utilized to process the non-aqueous lubricant for a metalworking operation in Y which the lubricant is collected and recycled after use,

e.g., the operation illustrated in FIG. 1. As shown schematically in FIG. 1, sprays of lubricant oil 11 are directed on the rolls 12 of a rolling mill, indicated generally by the reference numeral 13, the sprays being directed at or near the entrance of the workpiece 14 into the bite of the rolls 12. The used oil 11 cascades and drips down from the mill 13 and'the workpiece 14 into a sump 15 or other collection point where the oil 11 is preferably allowed to settle at least briefly to drop out larger dirt particles before it is pumped or otherwise conveyed to a treatment tank and reservoir 16.

If the lubricant does not already contain at least about 0.5 percent by weight monohydric alkanol, based on the weight of the oil, the same is added to the oil in the treatment tank. Preferably, the alkanol level is at least 1.5 percent by weight and at least 3 percent by weight is even more preferred for the purposes of this invention, but must beselected primarily with a view to the lubrication needs of the metalworking operation so that excessive amounts of alkanol may not be added arbitrarily and generally the concentration should be below 7 percent and more usually below about 6 percent.

Referring briefly to FIG. 2, particulate alkali metal hydroxide 17, e.g., KOH, in the form of particulate caustic potash, preferably as pellets, is placed in a foraminous enclosure 18 such as a wire mesh tube. The foraminous enclosure 18 is positioned in the lubricant oil 11 in the treatment tank or reservoir 16. A quantity of hydroxide is used which corresponds to an excess over that required to bring the total acid number (TAN) for the total charge of oil 11 in the system to less than 0.12 mg. KOH per gram of oil, The TAN is preferably determined according to ASTM method D974-58T. To accomplish more rapid change in the TAN, it is preferred to use from 5 to times the computed amount of hydroxide necessary to counteract the acidity in the system. In systems containing at least about l0,000 gallons of oil, corrective acidity changes may require from I to 6 weeks.

A 100 to 200 fold excess may be used to effect a rapid change in, e.g., about 30 minutes, especially in the presence of the higher molecular weight alkanols such as alkanols containing 12 or more carbon atoms.

The alkanol-soluble hydroxide of choice is caustic potash, i.e., KOH, because it is strongly basic and has some solubility even in the higher molecular weight alkanols. Caustic soda, i.e., NaOI-I, is a less expensive commodity and is usable, but is a slightly weaker base and exhibits a lower solubility in the alkanols. RbOH and CsOH are each more active bases and are more readily soluble than KOH and are suitable for use, although presently too expensive for regular commercial use.

After a TAN of 0.025 mg. KOH per gram oil or lower has been reached, the hydroxide l7 and the forminated enclosure 18 may be removed from the treatment tank 16 and re-introduced intermittently as required for acidity control, or the quantity of particulate hydroxide in the foraminated enclosure 18 can be reduced, to decrease the surface area of particulate hydroxide exposed to the oil and thereby cut down take-up of hydroxide and treatment with hydroxide can be maintained on a steady continuous basis. Generally, it is found necessary periodically to remove the foraminous enclosure 18 from the oil 11 and to empty out any gelatinous or clumped hydroxide particles resulting from take-up of water in the system, and to recharge the foraminous enclosure 18 with fresh dry particulate hydroxide.

A preferrecl'form of foraminous enclosure is a monel steel wire mesh filter tube although a wire gauze or screen enclosure may also be used, or, simply a cloth bag, made of burlap or coarse cotton duck, similar to that shown in FIG. 3.

If desired, and in the event the oil lubricant contains substantially no monohydric alkanol, the hydroxide may be dissolved in monohydric alkanol and the alcoholic solution added to the oil, e.g., in the treatment tank or reservoir 16, in the requisite amount to correct the acidity of all the oil in the system.

As the acidity of the oil is corrected towards a TAN less than about 0.12 mg. KOH per gram oil, the metal fines, in the case of aluminum, tend to dissolve and the oil is largely clarified. On reaching a TAN of about 0.025 mg. KOH per gram of oil, the color of the oil lightens considerably, and, in the case of the mineral oils, becomes a light golden yellow or amber color. Generally, it is sufficient to maintain a TAN of less than about 0.08 mg. KOH per gram of oil unless it is important to the mill operator to keep the oil in the light colored condition. Usually a very low TAN is not reachable unless the amount of particulate hydroxide used exceeds the theoretical amount needed by at least a five-fold excess since the surface area exposed is insufficient to get rapid enough reaction to attain the lower TAN.

The particulate hydroxide used may be in the form of flakes or pellets. Flakes provide a higher ratio of surface area to weight and increase reaction speeds but are rather sensitive to high moisture content in the oil in the case ofKOH, RbOI-I or CsOI-I, and tend to take up the water readily and form a gelatinous mass which seems to have little further beneficial effect on the oil. The pellets have less tendency to do this and are somewhat preferred.

The alkanol that forms the essential ingredient for the present reconditioning treatment, as indicated, may be already a component of the metalworking oil or it may be added if not such a component, or if present in insufficient amount. The alkanol may also be used as the vehicle for introducing the requisite amount of hydroxide as an alcoholic solution, although it is generally considered less hazardous to handle the particulate hydroxide.

Take-up of the solid particulate hydroxide into the oil occurs sufficiently rapidly for most operations when the monohydric alkanol content of the oil is about 0.5 percent by weight, but generally an alcoholic content of at least 1.5 percent is preferred, and about 3-6 percent is more preferred.

The monohydric alkanols or mixtures thereof that are used preferably have from 1 to about carbon atoms, although a mixture of lower molecular weight alkanols with higher molecular weight alkanols may be used if the temperature of the system is maintained slightly elevated above room temperature to avoid thickening of the oil and/or precipitation of the alkanol, e.g., a temperature of 50 to 100 F., generally at least about 80 F Thus, a mixture about half of which is a combination of 16 carbon atom alkanols and 18 carbon atom alkanols is usable wherein the remainder of the mixture is largefi fcoriibifiationbfl i carbon atom alkanols and 12 carbon atom alkanols.

In making deliberate additions of monohydric alkanol, it is preferred to add one or a combination of methanol, ethanol or isopropanol unless these interfere with the determination of higher alcohols present for metalworking purposes, in which case a decyl alcohol may be more preferred.

In a preferred manner of reconditioning used nonaqueous metalworking oil, the oil, after hydroxide treatment, is subjected to mechanical separation of solids therefrom as by filtration through a diatomaceous earth filter, or centrifugation. In such mechanical separation operations, there is removed, from the oil, solids precipitating as a consequence of the hydroxide treatment as well as any metal fines and soil sediment.

As shown in FIG. 1 schematically, the treated oil in treatment tank 16 may be pumped back by pump 19 to the spray nozzles at the mill which produce the sprays 10. On the other hand, on closing valve 20 and opening valves 21, 22, oil from the treatment tank 16 is filtered or centrifuged through mechanical separator 23, and the clean oil delivered to clean reservoir 24, from whence it is pumped by pump to the spray heads at the rolls 12 of the mill.

If desired, mechanical separation may be carried on as a by-pass operation instead of full flow, e.g., by only partially closing valve 20 and only partially opening valves 21 and 22. By-pass operations may be indicated when only a small filter is available or in the event the dirt load is relatively light and full flow operations are not needed to obtain adequate cleanliness.

Another manner of bringing the used oil into contact with particulate hydroxide is shown in the fragmentary view depicted in FIG. 4. In the embodiment there illustrated, oil 11 from sump 15 is pumped by pump 26 to reservoir 16 via a line controlled by line valve 27 and by-pass valve 28.

Oil conveyed through the by-pass is flowed through a charge 29 of particulate hydroxide contained in a vessel such as cylinder 30 and exits through a connecting conduit through valve 31 to the line leading to the reservoir 16.

Appropriate setting or closing of valves 27, 28 and 31 respectively, permits controllably passing all or a part of the oil 11 through the line or the by-pass. The proportions of oil flowed through the by-pass are dictated by the extent of need for treatment with particulate hydroxide.

EXAMPLES The following examples of the process of the invention are illustrative and the scope of the invention is not to be considered limited thereto.

EXAMPLE 1 A cold rolling mill lubricant was made up from 65 percent by volume Generex 57 oil (Mobile Oil Company), 32 percent by volume Texaco 1527 oil (Texas Oil Company) and 3 percent by volume of HT 45 alkanol mixture (Allegheny Refining Company). BT 45 a1- kanol mixture consists of about one-fourth C18 monohydric alcohol, about one-fourth C16 monohydric alcohol, nearly one-half C14 monohydric alcohol and a small amount of C12 monohydric alcohol. About 10,000 gallons of this lubricant was used and reused steadily for several months for cooling and lubricating the rolls of a single stand finishing mill used for cold rolling aluminum and the aluminum sheet rolled therein. The lubricant was initially a light golden color but promptly darkened and picked up a load of fines and other sediment.

A one gallon sample of the used lubricant was treated with a slight excess of alcoholic KOH (about 3 weight percent KOH in isopropanol) over that needed to bring the TAN to zero. In a short time, the lubricant turned a light gold, a similar color to the base mixture, but even after settling was slightly turbid. The treated lubricant was then filtered through I-Iyflo Super-Cel diatomaceous earth and a sample thereof was subjected to physical testing and analysis as was a sample of untreated used lubricant. The results of the tests are as follows:

On repeating the treatment of used lubricant as in Example 1 with a 3 percent KOI-I solution made using Lorol 5 a dodecyl alcohol, the same fine results were observed in lightening the color of the dark lubricant and in reducing the acid number. The KOH solution was made up by warming the pellets and the Lorol 5 together to a temperature of about 215 F. to obtain prompt dissolution.

EXAMPLE 3 A 3 percent solution of KOI-I in BT45 alkanol mixture was made up by heating the pellets and alkanol mixture together to a temperature of about 210 F. Used coolant at a temperature of about F. was lightened in color and its acid number reduced upon treating it with the KOH solution. However, the KOH solution solidified upon being allowed to cool to ambient room temperature and used coolant that was at ambient room temperature when mixed with the hot KOH solution showed precipitation of some solids upon subsequent cooling indicating that such treatment is best carried out only on lubricants while they are kept warm as in a circulating system in use.

EXAMPLE 4 Sufficient KOH pellets to more than reduce to zero the TAN of a sample of the used lubricant of Example 1 was added to the sample and the combination was heated to 100 F. for a time. Periodic observation showed that the color was slowly lightening in a slow controllable manner.

On adding a quantity of KOH pellets in the range of 100 to 200 fold excess needed to reduce the TAN to zero, the used lubricant turned amber within to minutes, showing that treatment can be carried out rapidly and terminated, if desired.

EXAMPLE 5 Sufficient KOH pellets to provide a substantial excess of that needed to bring to zero the TAN of two respec tive samples of the used lubricant described in Example 1 was added to each such sample by placing the pellets in a small cloth bag and suspending the bag in the lubricant. The one bag contained a ten-fold excess while the other contained a five-fold excess of KOH. After 30 days the sample exposed to a ten-fold excess lightened and turned amber indicating zero TAN while the sample exposed to a five-fold excess was still dark in color, but improving, indicating a slower reaction.

EXAMPLE 6 Fifty gallons of the used lubricant described in Example l was placed in a tank and an amount of KOH flakes sufficient to provide a ten-fold excess over that needed for zero TAN was placed in a cloth bag and suspended in the lubricant at room temperature for 36 days. The bag was removed and the contents inspected. The flakes had become a semi-solid gelled mass with relatively little surface area and provided for a very slow uptake of KOH that appeared adequate for a maintenance situation but not for a problem where prompt correction is needed.

A quantity of pellets of KOH sufficient to provide a thirty-fold excess of that needed for zero TAN was then placed in a Monel steel woven filter tube and suspended in the oil. Periodically the lubricant was sampled, the time noted and TAN determined according to ASTM D974-5 8T method. The results of sampling and testing are tabulated as follows:

Elapsed Time (Hrs) TAN,

,Fluctuations are explainable by assuming inadequate mixing before sampling and lack of precision of method.

The results show that a steady reaction is obtained that is readily controlled by removing the KOH from the lubricant on the one hand or by using a larger excess, on the other hand to speed up reaction.

EXAMPLE 7 Similar fine results in neutralizing and clarifying used metalworking oil are obtained on repeating the tests of Examples 4, 5 and 6 using, respectively, and successively, NaOl-I, RbOH and CsOH in place of KOH.

I claim:

1. The method of reconditioning used non-aqueous metalworking lubricant which consist essentially of a mineral oil containing solid particulate matter in the form of metal fines and non-metal fines, and, containinant water and/or acidity which comprises:

bringing sufficient monohydric alkanol-soluble alkali metal hydroxide, in a form selected from the group consisting of solid hydroxide and'a solution thereof in monohydric alkanol, into contact with the lubricant in the presence of an alkanol for a sufficient time to reduce the total acid number of the lubricant to less than about 0.12 mg. KOl-l per gram of lubricant, said alkanol being a monohydric alkanol or mixture of monohydric alkanols having a solubility of at least 0.5 percent by weight in the lubricant at a temperature of about F thereby to neutralize any acidity, take up any contaminant water into the hydroxide form, and to precipitate any suspended solid particulate matter in the lubricant.

2. The method as in claim 1 wherein sufficient alkali metal hydroxide is employed to reduce the total acid number to less than about 0.08 mg. KOH per gram of lubricant.

3. The method as in claim 1 wherein sufficient alkali metal hydroxide is added to reduce the total acid number of the lubricant substantially to zero.

4. The method as in claim 1 wherein the monohydric alkanol or mixture of monohydric alkanols contain from about 1 to about 10 carbon atoms per molecule.

5. The method as in claim 1 wherein the alkali metal hydroxide is added to the lubricant as a solution in the monohydric alkanol.

6. The method as in claim 1 wherein the alkali metal hydroxide and monohydric alkanol are brought separately to the lubricant and the alkali metal hydroxide is brought into contact with the lubricant by placing particulate hydroxide in a foraminous enclosure and placing said enclosure in the lubricant. v 7. The method as in claim 1 wherein the lubricant contacted by alkali metal hydroxide and monohydric alkanol is subjected to a mechanical separation process to remove solid precipitate formed as a consequence of the action of the alkali metal hydroxide.

8. The method as in claim 1 wherein the alkali metal hydroxide is a member selected from the group consist- I fines and non-metal fines, and, contaminant water and- /or acidity, which comprises:

placing a foraminous enclosure containing solid particulate alkali metal hydroxide in the lubricant until the total acid number of the lubricant is less than about 0.12 mg. KOl-l per gram of lubricant.

11. The method as in claim 10 when carried out so as to continuously maintain the total acid number of the lubricant less than about 0.12 mg. KOH per gram lubricant.

12. The method as in claim 10 wherein the so-treated lubricant is subjected to a mechanical separation process to remove solid precipitate formed in the lubricant as a consequence of placing the enclosure of alkali metal hydroxide therein.

13. The method of reconditioning used non-aqueous lubricant consisting essentially of a mineral oil containing a monohydric alkanol or mixture of monohydric alkanols and solid particulate matter in the form of metal fines and non-metal fines, and, contaminant water and- /or acidity, which comprises: circulating a stream of the lubricant through a charge of particulate alkanolsoluble alkali metal hydroxide held within an enclosed zone until the total acid number of the lubricant is less than about 0.12 mg. KOl-l per gram of lubricant.

14. The method as in claim 13 in which the alkali metal hydroxide is caustic potash. 

2. The method as in claim 1 wherein sufficient alkali metal hydroxide is employed to reduce the total acid number to less than about 0.08 mg. KOH per gram of lubricant.
 3. The method as in claim 1 wherein sufficient alkali metal hydroxide is added to reduce the total acid number of the lubricant substantially to zero.
 4. The method as in claim 1 wherein the monohydric alkanol or mixture of monohydric alkanols contain from about 1 to about 10 carbon atoms per molecule.
 5. The method as in claim 1 wherein the alkali metal hydroxide is added to the lubricant as a solution in the monohydric alkanol.
 6. The method as in claim 1 wherein the alkali metal hydroxide and monohydric alkanol are brought separately to the lubricant and the alkali metal hydroxide is brought into contact with the lubricant by placing particulate hydroxide in a foraminous enclosure and placing said enclosure in the lubricant.
 7. The method as in claim 1 wherein the lubricant contacted by alkali metal hydroxide and monohydric alkanol is subjected to a mechanical separation process to remove solid precipitate formed as a consequence of the action of the alkali metal hydroxide.
 8. The method as in claim 1 wherein the alkali metal hydroxide is a member selected from the group consisting of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide.
 9. The method as in claim 1 wherein the alkali metal hydroxide is brought into contact with the lubricant by circulating a portion of the lubricant through a charge of particulate alkali metal hydroxide held in an enclosed zone.
 10. The method of reconditioninG used non-aqueous lubricant consisting essentially of a mineral oil containing a monohydric alkanol or mixture of monohydric alkanols and solid particulate matter in the form of metal fines and non-metal fines, and, contaminant water and/or acidity, which comprises: placing a foraminous enclosure containing solid particulate alkali metal hydroxide in the lubricant until the total acid number of the lubricant is less than about 0.12 mg. KOH per gram of lubricant.
 11. The method as in claim 10 when carried out so as to continuously maintain the total acid number of the lubricant less than about 0.12 mg. KOH per gram lubricant.
 12. The method as in claim 10 wherein the so-treated lubricant is subjected to a mechanical separation process to remove solid precipitate formed in the lubricant as a consequence of placing the enclosure of alkali metal hydroxide therein.
 13. The method of reconditioning used non-aqueous lubricant consisting essentially of a mineral oil containing a monohydric alkanol or mixture of monohydric alkanols and solid particulate matter in the form of metal fines and non-metal fines, and, contaminant water and/or acidity, which comprises: circulating a stream of the lubricant through a charge of particulate alkanol-soluble alkali metal hydroxide held within an enclosed zone until the total acid number of the lubricant is less than about 0.12 mg. KOH per gram of lubricant.
 14. The method as in claim 13 in which the alkali metal hydroxide is caustic potash. 